FIG. 1 is a reduced complexity block diagram of a conventional system architecture for providing connectivity between a plurality of user terminals of a local area network and the internet. As shown therein, a plurality of end user communication terminals 110 are connected to associated ports 121 of an Ethernet-based distribution switch 120, which is typically configured as a managed layer two Ethernet switch, and is coupled to a processor (CPU 125)-controlled switch fabric chip 130 (such as a Broadcom BCM5645 Strataswitch) within a managed Ethernet switch subsystem 100. In the WAN direction, the switch fabric chip 130 is further coupled to an Ethernet port 140, which is coupled over a communication link 150 (configured as an IEEE 802.1Q trunk link) to an associated Ethernet port 201 of a layer three edge router subsystem 200.
Within the router subsystem 200, Ethernet port 201 is coupled to the router's communication control processor chip (CPU) 210 (such as a Freescale MPC866) which, in turn, is coupled to a wide area network port 220, that provides a digital communication interface to the internet 230, and to a dial back-up unit 240, that provides auxiliary connectivity to public switched telephone network 250.
Although the block diagram of FIG. 1 depicts only four user terminals 110 connected to the Ethernet-based distribution switch 120, it will be realized that in actuality the number of user terminals can expected to be in the thousands; only four are shown in order to reduce the complexity of the drawings. In order to handle data traffic among a large number of user terminals, advantage is taken of the ability of the managed layer two Ethernet distribution switch 120 to subdivide the LAN into multiple virtual LANs (VLANs), which increases the efficiency of the network by reducing the broadcast traffic load, as each VLAN provides virtual isolation of traffic between itself and other VLANs. Once traffic intended for the internet leaves a VLAN, it is the task of the layer three edge router subsystem to route the traffic from the VLAN to the WAN.
As shown in FIG. 1 and as described above, the managed Ethernet switch subsystem 100 and the edge router subsystem 200 are isolated subsystems that are tied together by way of an IEEE 802.1Q VLAN trunk, which is the physical link that transports information from multi VLANs to the WAN and vice versa. In accordance with the communication protocol employed by the system, each frame traversing the trunk has a VLAN tag prepended to the frame, so that traffic from one VLAN is distinguishable from traffic from all other VLANs.
In the conventional system of the type shown in FIG. 1, the user (system manager) is required to configure the VLAN trunk on both sides of the link 150 before traffic can flow from each VLAN to the WAN. This is a time-consuming and tedious task, that is prone to errors, particularly as the number of user terminals and VLANs increases.